How to beat COVID-19 with ‘Swiss cheese’
Each of the measures shown in the figure here–the “Swiss cheese model of prevention”–lowers the probability that an infectious dose of virus will find its way to your respiratory tract and, if it does, will actually cause an infection. Also, depending on the effectiveness and extent of vaccine administration, vaccination could make some of the other interventions superfluous.
Such strategies are the essence of preventive medicine. Many of us take drugs to lower our cholesterol levels or blood pressure to reduce the likelihood of cardiovascular disease and get flu vaccines to prevent the flu. Erecting barriers to prevent infection is well understood. What is harder is predicting what’s in store. That is, how the pandemic will evolve. There is a spectrum of possibilities, which are dependent upon probabilities. The virus could become less lethal and evolve into something endemic in the population, similar to other coronaviruses that cause colds, remain a serious threat, or become even more virulent.
Keeping in mind that the ultimate telos, or life goal, of pathogens is to “go forth and multiply,” there’s no particular advantage to killing their host. Arguably, a respiratory virus proliferates best when infected hosts are able to mix with other people and breathe on them; and the longer the asymptomatic, contagious period, the better for spreading infection.
Consider pandemics of influenza, the “flu” virus, to which COVID-19 is sometimes compared. Flu pandemics taper off when we reach herd immunity and enough of the population becomes immune, either through infection or vaccination and the virus has difficulty finding new, vulnerable hosts. For COVID-19, trying to attain immunity through natural infection is not a good option because of the high frequency of persistent symptoms — such as fatigue, fever, brain fog, and loss of taste or smell — in as many as 30% of people who recover from the acute infection.
One of the most vexing questions is the long-term effectiveness of the COVID-19 vaccines. Will they confer long-lasting protection, like the lifetime immunity after smallpox vaccination, or will immunity wane — for which there is some recent evidence?
Finally, public health officials and virologists are concerned about new, nasty mutants or “variants of concern” that will evade protection from the existing vaccines. Again, that’s a matter of probability, which increases with the number of COVID-19 infections, every one of which creates more mutants that Darwinian evolution will test for “fitness” – that is, the ability to spread and to overcome vaccine-induced or natural immunity.
We can lower the probability of exposures and infections with the interventions shown on the Swiss cheese figure. We should use them, especially those that are relatively painless.
Henry I. Miller, a physician and molecular biologist, is a Senior Fellow at the Pacific Research Institute. The co-discoverer of a key enzyme in the influenza virus, he was the founding director of the FDA’s Office of Biotechnology.
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